In order to carry out certain operations on a workpiece, which operations deviate from a 90.degree. angle, vises must be appropriately positioned with respect to one of the T-grooves of the machine table and must then be clamped. Various angle setting mechanisms are known for this positioning.
The most common angle setting mechanism consists in a so-called flat plate arranged below the vise base plate, which flat plate is provided with a graduation. The base plate itself is secured by screws which are screwed into anchor blocks in the T-grooves of the machine table. The base plate of the vise is in turn supported pivotally about a vertical axis on the flat plate and carries a zero line, which cooperates with the graduation. The base plate of the vise can in turn be clamped relative to the flat plate. Due to the elevated arrangement of said base plate on the flat plate, in which arrangement the base plate is also only partly supported by the flat plate, there is a considerable lessening in stability so that no great cutting pressures can be applied on the clamped workpiece and further the precision of the machining operation can be effected. It is further disadvantageous that each vise, with which there is any likelihood of utilization for machining operations at angles other than 90.degree. , must be equipped with a flat plate. Particularly, a later installing of the flat plate is not possible in most cases because the zero line of the base plate must be calibrated exactly on the flat plate. Since operations at other than a 90.degree. angle are not often carried out, it is not feasible to equip vises with a flat plate which will only seldom be used.
Furthermore bevels and protractors are known, the use of which in vises usually creates difficulties, because said measuring instruments are usually constructed of insufficient strength. They can deform and thus permit no exact adjustment. Moreover, the mentioned bevels and protractors have in most cases no part which directly engages one of the T-grooves of the machine table.